The 4/4 only had a servo fitted from 1991 onwards. In my 1990 4/4 4-seater I had it retrofitted in 2014, at the same time with an upgrade with Hi Spec dual twin calipers front brakes. Never heard of a 4/4 with twin filler caps.
Ruut Bianchi Morgan PlusFour 2023 Bentley Midnight Emerald Morgan 4/4 4-seater 1990 Royal Ivory